1.38
It is a noticeable difference in driving the car. The smaller primary is best used on a stock 340 for the largest engine. I used it on my ‘79/400 B engine. I did live with it for a while. It wasn’t bad. But it was very noticeable when I swapped the larger carb in.
In a performance small block oriented scenario, the 1.50 is what your going to appreciate driving around on. Always on a big block if you can.